Lieutenant Youji Itami is an otaku who joined the Japan Self-Defense Force largely to fund his hobby, and he is off duty in Ginza when a portal opens and an army of medieval soldiers and monsters pours out to attack Tokyo. The JSDF drives them back and marches through the Gate to build a base in the Special Region beyond. Itami leads the Third Reconnaissance Team into that world, where scouting a fantasy landscape turns into shielding its villagers from a dragon and from bandits.